Switch for optical signals

ABSTRACT

The invention relates to a switch ( 112 ) for optical signals and which has a number of outputs at least equal to the number of inputs and include means whereby an input signal is routed to at least one of those outputs. Each input receives information modulating optical carriers at different wavelengths. The switch ( 112 ) includes means ( 126   11   , 126   12 , . . . ,  126   NB ) for grouping all the carriers received into non-contiguous subsets of carriers (G 11 , . . . , G 1B , . . . , G N1 , . . . , G NB ) and means ( 129   1 ,  129   2 , . . . ,  129   NB ) for selecting blocks of carriers from the same subset of carriers. The information corresponding to each subset of optical carriers is thus routed in blocks to the same subset output. 
     Switching the carriers at the subset level improves the quality of the output signal and limits the number of components for the same total quantity of information switched.

The invention relates to a switch for optical signals and moreparticularly to a switch for packet signals.

Telecommunications are expanding considerably. More and more users(individuals and businesses) are transmitting an increasing number ofmessages in telecommunication networks. Also, the messages include anever-increasing quantity of information, for example when sendingpictures. To respond to this growing demand for information bit rate,telecommunications network operators are using optical signaltransmission, which modulates optical signals, generally produced bylasers, in accordance with the information to be transmitted, afterwhich the modulated signals propagate in a network of conductors oroptical fibers.

Transmitting signals optically has several advantages. In particular,the attenuation of the signal during transmission is less than in thecase of electrical signals and the bandwidth of optical fibers isgreater. It is therefore possible to transmit several carriers withdifferent wavelengths simultaneously in the same fiber. This technique,known as wavelength division multiplexing, achieves information bitrates of the order of 1 terabit/s.

In parallel with wavelength division multiplexing, time divisionmultiplexing enables simultaneous transmission of several calls on thesame carrier. In packet mode, each carrier transmits packets relating todifferent messages whose information has been divided up into packets,each packet being launched into the network with a header indicating itsdestination. When the packet passes through a switching device, thedevice dedicates resources to routing the packet during the time periodneeded to switch the packet to a requested output. Those resources arethen freed again for switching another packet. Because the packets areof limited duration, of the order of 1 microsecond, many calls can betransmitted in a short time period. This routing policy is currentlyused on the largest of all networks: the Internet.

Implementing switches using optical technology has been envisaged. Twotypes of switch can be distinguished:

cross-connect switches that set up semi-permanent connections betweentrunks routing a large number of multiplexed messages or calls, and

switches capable of routing calls or messages individually, i.e. thatcan be reconfigured for each new call or each new message.

The document JINNO M ET AL.: “ULTRA-WIDE-BAND WDM NETWORKS ANDSUPPORTING TECHNOLOGIES” CORE NETWORKS AND NETWORK MANAGEMENT,AMSTERDAM: IOS PRESS, NL, 1999, pages 90-97, XP000829416ISBN/90-5199-497-4 describes a cross-connect switch that receives andswitches, without demultiplexing them, optical signals consisting of 16carriers having different wavelengths. This switch cannot routeindividual calls or messages. Also, it is designed for very lowswitching speeds.

The invention relates to switches whose function is to route calls ormessages individually. Also, if the signals are transmitted in packetmode, the switch must route all the packets present at the respectiveinputs to designated outputs and then change configuration to routesubsequent packets.

FIG. 1 is a block diagram of a prior art switch 10 that implements theabove function. It has N inputs 10 ₁, 10 ₂, . . . 10 _(N) each of whichis adapted to be connected to a respective optical fiber 12 ₁ 12 ₂, . .. , 12 _(N). Each fiber transmits m channels consisting of m respectivecarriers at different wavelengths λ₁, λ₂, . . . , λ_(m) modulated bypulses and by packets.

Each input 10 ₁, 10 ₂, . . . 10 _(N) is connected to a respectivecorresponding optical demultiplexer 13 ₁, . . . , 13 _(N) whichseparates the m carriers received at that input. Each carrier is thentransmitted to a wavelength converter and regenerator device 18 ₁, . . ., 18 _(N). The converted signals are recombined by an opticalmultiplexer 14 ₁, . . . , 14 _(N). N signals G₁, G₂, . . . , G_(N) areobtained at the output of these multiplexers. The N signals are thenbroadcast in m.N directions by respective couplers 15 ₁, . . . , 15_(N). They are then routed to m×N respective outputs 20 ₁, 20 ₂, . . . ,20 _(mN) of the switch 10 by m×N respective selector units 22 ₁, 22 ₂, .. . , 22 _(mN). Each selector unit is in two parts, namely, for the unit22 ₁, for example, an input selector first device 24 ₁ and a wavelengthselector second device 24 ₂.

For example, the input selector device 24 ₁ has N inputs each of whichis connected to respective outputs 16 ₁ to 16 _(N) of the converter andregenerator devices 14 ₁, 14 ₂, . . . 14 _(N). The input selector device24 ₁ selects at most one of the N received signals G₁, G₂, . . . ,G_(N). The selected signal is then routed to the wavelength selectordevice 24 ₂. From the m carriers of the signal selected, the latterdevice selects one carrier to be transmitted to an output 20 ₁ of theswitch 10. The signals supplied at the outputs 20 ₁, 20 ₂, . . . , 20_(mN) are then grouped into groups of m signals having differentwavelengths λ₁, λ₂, . . . , λ_(m) by multiplexers 14 ₁, . . . , 14 _(N)so that they can be transmitted via optical fibers 13 ₁, . . . , 13_(N).

In other embodiments, the number of output fibers and the number ofchannels per output fiber can be different from N and m, respectively.On the other hand, the total number m.N of output channels is equal tothe total number of input channels.

Each input selector device 24 ₁, etc. includes at least N selectorunits, for example optical amplifiers used as optical gates. Eachwavelength selector device 24 ₂, etc. includes at least m selector unitsconsisting of optical amplifiers used as optical gates, for example, andwavelength-selective means. The switch 10 therefore includes at leastm.N.(m+N) optical amplifiers. This large number of components is notfavorable to reliability, simplicity or optimum fabrication cost. Also,each signal G₁, G₂, . . . , G_(N) is broadcast to an input of each ofthe m.N input selector units 22 ₁, 22 ₂, . . . , 22 _(mN). A consequenceof this is that the power of each signal G_(i) is divided by a factorm.N.

Furthermore, after the selection effected by the first device 24 ₁, theselection operated by the second device 24 ₂ further divides the powerof the signal by a factor equal at most to a value from N to m.Accordingly, in total, the power of each input signal is attenuated byat least a factor N.m.max(N,m). This reduction in the power of thesignals in the selector device produces a low signal/noise ratio andtherefore distortion, which becomes problematic for signals at very highbit rates, for example bit rates higher than 10 Gbit/s.

An object of the invention is to reduce significantly the number oftimes each signal is divided for the same total bit rate processed inthis kind of switch. This increases the signal/noise ratio and higherinformation bit rates can therefore be achieved.

The invention provides a switch for optical signals, the switchincluding a number of outputs at least equal to the number N of inputs,for routing an input signal to at least one output, each input beingadapted to receive signals modulating optical carriers having mdifferent wavelengths, characterized in that it includes:

means for grouping all of the carriers received at an input of theswitch into non-contiguous subsets of carriers;

selector units for routing in blocks the signals corresponding to eachsubset of optical carriers; and

means for dividing each subset and then transmitting all the carriers ofthat subset to the same output of the switch.

The above switch processes a whole subset of the set of wavelengths,i.e. a plurality of wavelengths, simultaneously, enabling the samesingle component to be used for each function, such as amplification andswitching, instead of one component for each wavelength, and thisapplies up to the destination output. Accordingly, the signals aredivided less than in the conventional optical switch shown in FIG. 1.

In the prior art switch, the factor by which the power of each carrieris divided is m×N before the input selector device 24 ₁. Between theinput selector device 24 ₁ and a wavelength selector second device 24 ₂,the division factor is whichever is the greater of m and N. Theembodiments of the invention show that in the switch according to theinvention the division factor is reduced to N×B before the inputselector stage and to B between the input selector stage and the stagefor selecting the subset of wavelengths, B being the total number ofsubsets of carriers per optical fiber. For example, if the set ofcarriers comprises 16 carriers (m=16), and if each subset includes fourcarriers (B=4), the factor by which each signal is divided will be lessthan in the prior art switch shown in FIG. 1 by the following amount:$\frac{m \cdot {{Max}( {N,m} )}}{B^{2}} = {\frac{16 \times 4}{4 \times 4} = 4}$

One particular embodiment of the switch according to the invention ischaracterized in that it further includes:

means for grouping all the subsets of carriers into non-contiguousgroups of subsets;

means for routing in blocks the information corresponding to a pluralityof subsets of carriers; and

means for selecting a single subset of carriers per output of theswitch.

The above switch processes a plurality of subsets of carriers at thesame time, enabling the same single component to be used for eachfunction, such as amplification and switching, instead of one componentfor each subset.

Other features and advantages of the invention will become apparent inthe course of the following description of embodiments of the invention,which description is given with reference to the accompanying drawings,in which:

FIG. 1, already described, is a block diagram of a prior art opticalswitch.

FIG. 2 is a block diagram of a first embodiment of an optical switchaccording to the invention, using subsets of carriers.

FIG. 3 is a block diagram of a second embodiment of an optical switchaccording to the invention, using groups of subsets of carriers.

FIGS. 4, 5, 10, 11, 12, 13 are block diagrams of various embodiments ofswitching means that can be used in the second embodiment.

FIGS. 6 to 9 are block diagrams of different variants of one portion ofthe embodiment shown in FIG. 5.

FIG. 2 is a block diagram of a first embodiment of a switch 112 inaccordance with the invention. It has N inputs each connected to anoptical fiber 110 ₁, 110 ₂, . . . , 110 _(N) transmitting wavelengthdivision multiplexed signals. Each optical fiber transports m carrierswith different wavelengths λ₁, λ₂, . . . , λ_(m). Each carriertransports a series of messages, each message having a differentdestination. The switch must therefore be configured differently foreach message. There are two techniques which can be used to groupcarriers in the same subset of carriers:

grouping different messages having the same destination, or

grouping message segments within the same message.

It is also possible to combine the above two techniques. To be moreprecise, the second technique entails dividing each message into aplurality of parts, each of which parts is transmitted by a carrier at adifferent wavelength from those of the other carriers transmitting theother parts of the message. The carriers being transmittedsimultaneously to the same destination, they form within each opticalfiber a subset of carriers to be routed to the same output.

In the embodiment shown in FIG. 2, all the optical fibers transmitexactly the same number m of carriers and the messages have already beendivided upstream of the switch, i.e. in the network. A differentembodiment could include a time-division demultiplexer at the input ofthe switch to distribute a message at bit rate D across f carriershaving different wavelengths and each having a bit rate D/f, with atime-division multiplexer at the output of the switch to reconstitutethe message on a single carrier at bit rate D.

For example, for the m carriers arriving via the fiber 110 ₁, the switch112 uses B subsets of carriers S₁₁, . . . , S_(1B). For the m carriersarriving via the fiber 110 _(N), the switch 112 uses B subsets ofcarriers S_(N1), . . . , S_(NB). In this example, all subsets comprisem/B signals with m/B respective different wavelengths λ₁, λ₂, . . . ,λ_(m/B).

Each input of the switch 112 is connected to a respectivesynchronization device 114 ₁, 114 ₂, . . . , 114 _(N) whose function isto synchronize all packets transported by the carriers arriving at thatinput with a clock (not shown) of the switch, in order for the whole ofthe switch to function synchronously. The output of each synchronizationdevice 114 ₁, 114 ₂, . . . , 114 _(N) is connected to the input of acorresponding optical demultiplexer 115 ₁, 115 ₂, . . . , 115 _(N), forexample using an interference filter, for separating the m carriersreceived at each input, restoring them at m respective outputs. Those mcarriers are then grouped into B subsets S1 ₁, . . . , SN_(B) eachconsisting of m/B carriers.

Each subset S1 ₁, . . . , SN_(B) of carriers is transmitted to arespective wavelength converter and regenerator device 124 ₁, . . . ,124 _(NB). Each converter and regenerator device includes, for each ofm/B carriers it receives, a regenerator that amplifies and reshapes theoptical pulses of the signal. It further includes a wavelength converterthat changes the wavelength of the carrier.

For example, the converter and regenerator device 124 ₁ receives m/Bcarriers with respective wavelengths λ₁, λ₂, . . . , λ_(m/B) andrestores m/B carriers with respective wavelengths λ′₁, λ′₂, . . . ,λ′_(m/B). The converter and regenerator device 124 _(B) receives m/Bcarriers with respective wavelengths λ_(m−(m/B)+1), . . . , λ_(m) andrestores m/B carriers with respective wavelengths λ′₁, λ′₂, . . . ,λ′_(m/B). Accordingly, the output wavelengths of all the wavelengthconverters of the converter and regenerator devices 124 ₁, . . . , 124_(NB) are exactly the same, for all the subsets of carriers S₁₁, . . . ,S_(1B).

Subsets of carriers having the same wavelengths λ′₁, . . . , λ′_(m/B)are therefore obtained. This simplifies the fabrication of the opticalswitch in accordance with the invention because the number ofwavelengths processed afterwards is reduced from m to m/B, for exampleenabling the use of amplifiers operating with a narrower wavelengthwindow than in the prior art switch. They are therefore less costly.

The carriers of the subsets S₁₁, . . . , S_(NB) obtained at the outputsof the respective regenerator devices 124 ₁, . . . , 124 _(NB) aregrouped by a respective multiplexer 126 ₁₁, . . . , 126 _(NB), each ofthese multiplexers corresponding to one subset of carriers. Thus at theoutput of the multiplexers 126 ₁₁, 126 ₁₂, . . . , 126 _(NB) a total ofN×B signals G₁₁, . . . , G_(1B), . . . , G_(N1), . . . , G_(NB) areobtained, each corresponding to one subset of carriers.

In this example, a subset of carriers transmits a message that isdivided into several parts, and each part of which is transmitted on onecarrier of the subset. The carriers relating to the same message aretherefore grouped into a single signal G_(ij). It is then possible toroute all the parts of the message to the same output fiber 146 ₁, . . ., or 146 _(N) by routing the signal G_(ij) to that fiber.

The signals G₁₁, . . . , G_(1B), . . . , G_(N1), . . . , G_(NB) from themultiplexers 126 ₁₁, 126 ₁₂, . . . , 126 _(NB) are amplified byerbium-doped fiber amplifiers 128. This type of amplifier has theadvantage of amplifying the signals with a signal/noise ratio and anoutput power much higher than those of semiconductor optical amplifiers.After they have been amplified by the amplifiers 128, the signals G₁₁, .. . , G_(1B), . . . , G_(N1), . . . , G_(NB) are broadcast by Nrespective broadcasters 115 ₁, . . . , 115 _(N) and then routed to theselector units 122 ₁, 122 ₂, . . . , 122 _(NB) by means of opticalfibers or optical conductors such as planar waveguides (to be moreprecise planar optical couplers).

Each selector unit 122 ₁, . . . , 122 _(NB) includes:

a respective switching device 129 ₁, . . . , 129 _(NB) which selects oneof the subsets of carriers from the N.B subsets broadcast by thebroadcasters 115 ₁, . . . , 115 _(NB); and

a demultiplexer 142 ₁, . . . , 142 _(NB) which separates the m/Bcarriers with wavelengths λ′₁, λ′₂, . . . , λ′_(m/B) of the respectivesubset 129 ₁, . . . , 129 _(NB) selected by the space switching device,and which applies those carriers to m/B respective converter andregenerator devices 145 ₁₁, . . . , 145 _(1m/B).

Each space switch device 129 _(i) includes:

A set of NB delay units 130 _(ij) for assigning to each signal receiveda time-delay that is a function of its priority. The priority order isincluded in the signal Gij itself, for example. The higher the priority,the shorter the time-delay.

A set 132 _(i) of NB optical gates for choosing only one of the delayedsignals and therefore validating only one input of the space switchingdevice 129 _(i). The gates consist of semiconductor optical amplifiers.A semiconductor optical amplifier, whether its gain is constant or not,is activated when the signal that it receives must be selected fortransmission. Only one gate is activated at a time. Note that the delayunits 130 _(ij) retain the signals that have not been selected. In theabsence of these delay units, the unselected signals would be lostirrecoverably.

A switched amplifier device 134_(i) having NB inputs connected torespective outputs of the set of gates 132 _(i). Its role is to impartto the transmitted signal sufficient power at the stage of recombiningthe outputs of the various optical gates 132 _(i) in a way that avoidsaddition of optical noise from the amplifiers. The output of theamplifier device 134 _(i) constitutes an output 140 _(i) of the spaceswitching device 129 _(i).

Accordingly, compared to the prior art switch shown in FIG. 1, the totalnumber of selection operations is reduced, since the number of selectorunits 122 ₁, . . . , 122 _(NB) is N×B whereas in the prior art switchthe total number of selector units is N×m, B being a submultiple of m.In other words, processing the carriers of a subset at the some time andtransmitting them at the same time considerably simplifies theimplementation of the optical switch, can reduce the number ofcomponents, and improves signal processing quality.

The total number of selector units 122 ₁, 122 ₂, . . . , 122 _(NB) isN.B and each selector unit 122 _(i) has N.B inputs. Each signal Gij isapplied to a corresponding input ij of each selector unit 122 ₁, 122 ₂,. . . , 122 _(NB). Accordingly, the signal G₁₁ coming from an output ofone of the amplifiers 128 is transmitted to the inputs indexed 11 of theselector units 122 ₁, 122 ₂, . . . , 122 _(NB). Each input of eachselector unit is associated with a delay unit 130 ₁₁, . . . , 130 _(N)_(²) _(B) _(²) for assigning to each received signal a time-delay thatis a function of its priority. The priority order is included in thesignal Gij itself, for example. The higher the priority the shorter thetime-delay.

The demultiplexer 142 _(i) therefore supplies at m/B outputs thecarriers of a subset of carriers whose wavelengths are respectively λ′₁to λ′_(m/B). Then, each carrier is processed individually by arespective wavelength converter and regenerator device 145 ₁₁, 145 ₁₂, .. . , 145 _(Nm) implementing functions similar to those of a converterand regenerator device 124 ₁, . . . , 124 _(NB). Each includes aconverter for modifying the wavelengths of the carriers so that mcarriers with different wavelengths λ₁, λ₂, . . . , λ_(m) can betransmitted in the same fiber.

A respective multiplexer 150 ₁, 150 ₂, . . . 150 _(N) combines mcarriers with wavelengths λ₁, λ₂, . . . λ_(m) provided by B selectorunits 122 _(i) so that each output fiber 146 ₁ to 146 _(N) actuallytransmits the m carriers on the m input wavelengths. Note that thenumber of output wavelengths is generally equal to the number of inputwavelengths and that each wavelength λ_(i) received at the input appearsat the output. However, it is possible to choose output wavelengthvalues that are different from the input wavelength values.

FIG. 3 is a block diagram of a second embodiment 212 using N′ groups ofB′ subsets of B carriers. For example, the switch 212 groups the mcarriers arriving via the input fiber 110 ₁ into B subsets S₁₁, . . . ,S_(1B) each comprising m/B carriers. Each groups the m carriers arrivingvia the input fiber 110 _(N) into B subsets S_(N1), . . . , S_(NB). Allthe subsets comprise m/B signals having m/B respective differentwavelengths λ₁, λ₂, . . . , λ_(m/B).

The switch 212 then groups these NB subsets into N′ groups eachincluding B′ subsets of carriers. For example, in the embodiment shownin FIG. 3, N′=N and B′=B. The group SG₁ therefore includes the subsetsS₁₁, . . . , S_(1B). The group SG_(N) includes the subsets S_(N1), . . ., S_(NB).

Components that are similar to those of the switch 112 carry the samereference numbers. The switch 212 has:

N inputs each connected to an optical fiber 110 ₁, 110 ₂, . . . , 110_(N) transmitting wavelength division multiplexed signals;

N synchronization devices 114 ₁, 114 ₂, . . . , 114 _(N) analogous tothose of the switch 112 (FIG. 2);

N wavelength converter and regenerator devices 124 ₁, . . . , 124 _(NB)analogous to those of the switch 112 (FIG. 2);

N multiplexer devices 226 ₁, . . . , 226 _(N);

N optical amplifiers 228;

N broadcasters 215 ₁, . . . , 215 _(N);

N selector units 222 ₁, . . . , 222 _(NB);

N.m wavelength converter and regenerator devices 145 ₁, . . . , 145_(Nm) analogous to those of the switch 112 (FIG. 2);

N optical multiplexers 150 ₁, . . . , 150 _(N) analogous to those of theswitch 112 (FIG. 2); and

N outputs each connected to an optical fiber 146 ₁, 146 ₂, . . . , 146_(N) transmitting wavelength division multiplexed signals.

Each selector unit 222 ₁, . . . , 222 _(NB) has:

N inputs connected to N respective outputs of N amplifiers 228 supplyingN respective signals H₁, . . . , H_(N); and

m/B outputs connected to m/B respective inputs of one of the wavelengthconverter and regenerator devices 145 ₁₁, . . . , 145 _(Nm).

This embodiment differs from the first one in that the broadcast stageincludes N multiplexers 226 ₁, 226 ₁, . . . , 226 _(N) with m inputs andN amplifiers 228 instead of N.B multiplexers 126 ₁, . . . , 126N withm/B inputs and N.B amplifiers 128. However, additionally, the NBselector units 222 ₁, . . . , 222 _(NB) are different because they areoptimized to exploit further the fact that the subsets of carriers aregrouped together. Each selector unit 222 ₁, . . . , 222 _(NB) can selecta plurality of subsets of carriers simultaneously, and not only onesubset, as in the switch 112.

FIG. 4 is a block diagram of a first embodiment 222 _(1a) of theselector unit 222 ₁ taken by way of example, for N=N′=16. It includes:

N optical gates 41 ₁, . . . 41 _(N), connecting N respective inputs ofthe unit 222_(1a) to a coupler 42 having N inputs and one output;

an optical erbium-doped fiber optical amplifier 43 having an inputconnected to the output of the coupler 42;

a demultiplexer 44 having an input connected to the output of theamplifier 43 and having N outputs;

m optical gates 45 ₁, . . . , 45 _(m) connected to respective outputs ofthe demultiplexer 44; and

m/B multiplexers 46 ₁, . . . , 46 _(m/B) each with B inputs and oneoutput, each input being connected to a respective output of thedemultiplexer 44 and the m/B outputs of the demultiplexers constitutingthe outputs of the selector unit 222 _(1a).

The gates 41 ₁, . . . , 41 _(N) are used to select a group of subsets ofcarriers from SG₁, . . . , SG_(N). In the example shown, N is equal to16. The gates 451, . . . , 45N select m/B carriers and supply them tothe m/B respective multiplexers 461, . . . , 46m/B. The number of inputsof each multiplexer 461, . . . , 46m/B is chosen to be equal to thenumber of carriers per subset (which is four, in the example shown inthis figure).

FIG. 5 is a block diagram of a second embodiment 222 _(1b) of theselector unit 222 ₁ taken byway of example, for N=N′=16. It includes:

N optical gates 50 ₁, . . . , 50 _(N) divided into groups of N/p; eachgroup of N/p gates connects N/p respective inputs of the unit 222 _(1b)to a coupler 51 ₁, . . . , 51 _(p) having N/p inputs and one output (thefigure shows an example in which p=4 and N=16);

p optical gates 52 ₁, . . . , 52 _(p) having their inputs connected torespective outputs of couplers 51 ₁, . . . , 51 _(p);

a coupler 53 having p inputs connected to respective outputs of thegates 52 ₁, . . . , 52 _(p) and having B outputs;

B optical gates 54 ₁, . . . , 54 _(B) having their inputs connected torespective outputs of the coupler 53; and

a demultiplexer device 55 having B inputs connected to respectiveoutputs of the optical gates 54 ₁, . . . , 54 _(B) and having m/Boutputs constituting the outputs of the unit 222 _(1b).

This embodiment of the switch in accordance with the invention requiresfewer optical gates than the prior art switch shown in FIG. 1. Eachselector unit has N+2.B optical gates, i.e. a total of N.B.(N+2B) gatesfor the whole of the switch. Under these conditions, if N=16 and B=4,the total number of gates is 1 536. In a conventional switch, for whichN=16 and m=16, the number of optical gates used for each selector unitis m.N. (m+N)=8 192.

Accordingly, in this example, the number of optical amplifiers of theswitch according to the invention is one fifth that of the prior artswitch, all other things being equal.

In the example shown in FIG. 5, N=16 and B=p=4. FIGS. 6 to 9 are blockdiagrams of different embodiments of the demultiplexer device 55 whenm=16 and B=4.

FIG. 6 shows an embodiment 55 a including:

a first stage of B demultiplexers each having one input and m/B outputs;and

a second stage of m/B couplers each having B inputs connected to arespective output of each of the demultiplexers of the first stage andhaving m/B outputs constituting the outputs of the device 55 a.

FIG. 7 shows an embodiment 55 b including:

a first stage of B demultiplexers each having one input and m/B outputs;and

a second stage of m/B multiplexers each having B inputs connected to arespective output of each of the demultiplexers of the first stage andhaving m/B outputs constituting the outputs of the device 55 b.

FIG. 8 shows an embodiment 55 c including:

if the subsets of carriers correspond to adjacent wavelengths:

a first stage consisting of a wavelength band multiplexer having Binputs and one output; these inputs constitute the inputs of the device55 c; and

a second stage consisting of a carrier interleaver having one input andm/B outputs, the inputs of this interleaver being connected torespective outputs of the first stage and its outputs constituting theoutputs of the device 55 c; or

if the subsets of carriers correspond to interleaved wavelengths:

a first stage consisting of a carrier interleaver having B inputs andone output; these inputs constitute the inputs of the device 55 c; and

a second stage consisting of a wavelength band multiplexer having oneinput and m/B outputs, the inputs of this multiplexer being connected tothe outputs of the first stage and its outputs constituting the outputsof the device 55 c.

FIG. 9 shows an embodiment 55 d including an array of waveguides havingat least m waveguides in its internal structure. The array must have atleast B inputs and m/B outputs, m/B of those outputs constituting theoutputs of the device 55 c. Note that, depending on the respectivearrangements of the inputs and outputs used, this device can demultiplexsubsets of carriers corresponding to adjacent or interleavedwavelengths.

FIG. 10 is a block diagram of a third embodiment 222 _(1c) of theselector unit 221 ₁ considered by way of example. In this example, thenumber N of groups is equal to 8 and the number N′ of subsets per groupof subsets of carriers is equal to 2. The unit includes:

a space selector stage consisting of N optical gates 201 ₁, . . . , 201_(N) divided into groups of N/p; the gates are connected to N respectiveinputs of the unit 222 _(1c);

p couplers 202 ₁, . . . , 202 _(p) each having N/p inputs and oneoutput; the inputs are connected to N/p respective outputs of a group ofoptical gates 201 ₁, . . . , 201 _(N) of the space selector stage;

a cyclic first array of waveguides 203 having q inputs, where q isgreater than p; p of the q inputs of the array are connected to prespective outputs of the couplers 202 ₁, . . . , 202 _(p);

a carrier subset selector stage consisting of B optical gates 204 ₁, . .. , 204 _(B) having their inputs connected to B respective outputs ofthe array 203;

m/B couplers 205 ₁, . . . , 205 _(p) each having B²/m inputs and oneoutput, the B²/m inputs being connected to respective outputs of thearray of waveguides 203 via optical gates 204 _(i); and

a cyclic second array of waveguides 206 having m/B inputs connected tom/B respective outputs of the couplers 205 ₁, . . . , 205 _(m/B) andhaving m/B outputs constituting the outputs of the unit 222 _(1c).

In the examples shown, N′=2, N=8, B′=2, B=4, p=4, q=5, m=8. The numbersm/B and q must be prime to each other. FIG. 10 shows how this embodimentworks in the case of routing a subset S₂₄ consisting of two carriers λ₄and λ₉ from eight carriers λ₁, λ₂, λ₃, λ₄, λ₆, λ₇, λ₈, λ₉ arriving atthe second optical gate 201 ₂. The references of the carrierstransmitted are indicated near the outputs of the components. Theoutputs of the array 203 can respectively restore the following subsetsof carriers:

S₂₁: λ₁, λ₆

S₂₂: λ₂, λ₇

S₂₃: λ₃, λ₈

S₂₄: λ₄, λ₉

The subset of carriers λ₅, λ₁₀ is not included in this example becauseit leads to an unused output of the array 203.

The outputs of the array 206 can respectively restore the followingcarriers:

λ₂, λ₄, λ₆, λ₈, λ₁₀

λ₁, λ₃, λ₅, λ₇, λ₉

The gate 201 ₂ selects all the carriers λ₁, λ₂, λ₃, λ₄, λ₆, λ₇, λ₈, λ₉arriving at that optical gate. It is controlled so that it allows thosecarriers to pass through it. The other gates 201 _(i) are shut. Thearray 203 restores only the carriers λ₄ and λ₉ at its output connectedto the gate 204 _(B). The gate 204 _(B) is controlled to allow thosecarriers to pass through it. The other gates 204 _(i) are shut. Thecoupler 205 _(m) transmits the carriers λ₄, λ₉ together to the array206. That array demultiplexes them and restores them on two separateoutputs.

FIG. 11 shows the same embodiment as FIG. 10, but indicates how it worksin the case of routing other carriers, applied to the gate 202 ₃,grouped into subsets S₃₁, S₃₂, S₃₃, S₃₄, as follows:

S31: λ₂, λ₇

S32: λ₃, λ₈

S33: λ₄, λ₉

S34: λ₅, λ₁₀

The comb of carriers is shifted for each input port of the array 203.Consequently, the comb of carriers arriving at the gate 201 ₃ is λ₂, λ₃,λ₄, λ₅, λ₇, λ₈, λ₉, λ₁₀. The subset of carriers λ₆, λ₁₁ is not includedin this example because it leads to an unused output of the array 203.

The gate 201 ₃, for example, selects all the carriers λ₂, λ₃, λ₄, λ₅,λ₇, λ₈, λ₉, λ₁₀ arriving at the optical gate 201 ₃. In this example, itis controlled so that it allows those carriers to pass through it. Theother gates 201 _(i) are shut. In this example, the carriers λ₃ and λ₈can be transmitted via the port of the array 203 that is connected tothat gate. The array 203 restores only the carriers λ₃ and λ₈ at itsoutput connected to the gate 204 ₂. The gate 204 ₂ is controlled so thatit allows those carrier to pass through it. The other gates 204 _(i) areshut. The coupler 205 ₁ transmits the carriers λ₃ and λ₈ together to thearray 206. That array demultiplexes them and restores them on twoseparate outputs.

This embodiment of the switch according to the invention requires feweroptical gates than the prior art switch shown in FIG. 1. Each selectorunit includes N+B optical gates, i.e. a total of N.B.(N+B) gates for thewhole switch. Under these conditions, if N=16 and B=4, the total numberof gates is 1 280. In a conventional switch, for which N=16 and m=16,the number of optical gates used for each selector unit is:

m.N.(m+N)=8 192.

Accordingly, in this example, the number of optical amplifiers of theswitch according to the invention is less than one sixth of that in theprior art switch, all other things being equal.

FIG. 12 is a block diagram of a fourth embodiment 222 _(1d) of theselector unit 222 ₁ considered by way of example, for N=16, B=16. Itincludes:

a space selector stage consisting of N optical gates 301 ₁ . . . , 301_(N), divided into groups of N.B/q each corresponding to a comb ofwavelengths C₁, . . . , C_(q/B) (a group of subsets of carriers);

q/B couplers 302 ₁, . . . , 302 _(q/B) each having N.B/q inputs and Boutputs, the inputs of each coupler being connected to the outputs ofthe optical gates 301 ₁, . . . , 301 _(N);

q optional optical filters 303 ₁, . . . , 303 _(q) connected to qrespective outputs of the couplers 302 ₁, . . . , 302 _(q/B);

a stage for selecting a subset of carriers, consisting of q opticalgates 304 ₁, . . . , 304 _(q) having inputs connected to respectiveoutputs of the filters 303 ₁, . . . , 303 _(q); and

a demultiplexer 305 having q inputs connected to q respective outputs ofthe gates 303 ₁, . . . , 303 _(q) and having at least m/B outputsconstituting the outputs of the selector unit 222 _(1d); q is chosen tobe greater than m.

The demultiplexer 305 can be implemented with an array of waveguides orwith an optical filter in a “modified Littman-Metcalf” configuration.The q band-pass optical filters 303 ₁, . . . , 303 _(q) increase thepower provided by the optical amplifiers constituting the gates byeliminating carriers of no utility from the subsets of wavelengths notrequired. Without these filters, the latter would consume some of theavailable power.

In the preferred embodiment, shown in FIG. 12, the filters are band-passfilters and the bands can therefore be adjacent. Each comb ofwavelengths C₁, . . . , C_(q/B) is shifted relative to the next comb byfour wavelengths so that the array 305 routes the wavelengths of eachcomb correctly. The number q of inputs (and outputs) of the array 305 isequal to 16. Only m/B outputs are used to constitute the outputsconnected to wavelength converter and regenerator devices 306 ₁, . . . ,306 _(m/B). Thus q-(m/B) outputs of the array 305 are not used.

It is possible to use those outputs more completely, given that accessto the array 305 is bidirectional. It is possible to use the unusedoutputs as inputs in this fourth embodiment and also in the thirdembodiment (FIGS. 10 and 11).

For example, FIG. 13 is a block diagram of a variant of the fourthembodiment of the selector unit 222 _(1d) for N=16, B=16. This variantuses the same array 310 for two switching stages SS_(2h) and SS_(2h+1),the array being used bidirectionally. The switching stage SS_(2h)includes:

a spatial selector stage consisting of N optical gates 301′₁, . . . ,301′_(N) divided into groups of N.B/q gates each corresponding to onecomb of wavelengths;

q/B couplers 302′₁, . . . , 302′_(q/B) each having N.B/q inputs and Boutputs, the inputs of each coupler being connected to respectiveoutputs of a group of N.B/q optical gates 301′₁, . . . , 301′_(N);

q optional optical band-pass filters 303′₁, . . . , 303′_(q) connectedto q respective outputs of the couplers 302′₁, . . . , 302′_(q/B);

a stage for selecting a subset of carriers, consisting of q opticalgates 304′₁, . . . , 304′_(q) having inputs connected to respectiveoutputs of the filters 303′₁, . . . , 303′_(q); and

a demultiplexer consisting of an array of waveguides 310 having q′ portson the left-hand side, constituting:

q inputs connected to q respective outputs of the gates 303′₁, . . . ,303′_(q), and

q′-q outputs, of which m/B outputs constitute the outputs of the stageSS_(2h+1), and can be connected to wavelength converter and regeneratordevices 306″₁, . . . , 306″_(m/B); q is chosen to be greater than m.

The switching stage SS_(2h+1) includes:

a space selector stage consisting of N optical gates 301″₁, . . . ,301″_(N) divided into groups of N.B/q gates each corresponding to onecomb of wavelengths;

q/B couplers 302″₁, . . . , 302″_(q/B) each having N.B/q inputs and Boutputs, the inputs of each coupler being connected to respectiveoutputs of a group of N.B/q optical gates 301″₁, . . . , 301′_(N);

q optional optical band-pass filters 303″₁, . . . , 303″_(q) connectedto q respective outputs of the couplers 302″₁, . . . , 302″_(q/B);

a stage for selecting a subset of carriers consisting of q optical gates304″₁, . . . , 304″_(q) having inputs connected to respective outputs ofthe filters 303″₁, . . . , 303″_(q); and

a demultiplexer consisting of the array of waveguides 310, crossed inthe opposite direction, its right-hand side having q′ portsconstituting:

q inputs connected to q respective outputs of the gates 303′₁, . . . ,303′_(q), and

q′-q outputs of which m/B outputs constitute the outputs of the stageSS_(2h), and can be connected to wavelength converter and regeneratordevices 306′₁, . . . , 306′_(m/B).

It will be evident to the skilled person how to modify the thirdembodiment shown in FIG. 10 in an analogous way to use the same array ofwaveguides for at least two separate switching stages.

One embodiment of the combs of wavelengths can include wavelengthsdistributed regularly; for example each subset includes four carrierswith intervals all equal to 100 GHz. To reduce intermodulation phenomenadue to non-linearities in the response of the amplifiers, it may beadvantageous to distribute the carriers in a less regular manner, forexample with each subset including four carriers with intervals of 100GHz, 200 GHz and 100 GHz, two adjacent subsets being separated by 100GHz. In another example, each subset includes four carriers withintervals of 200 GHz, 100 GHz, 100 GHz and two adjacent subsets areseparated by 100 GHz.

What is claimed is:
 1. A switch (112) for optical signals, the switchincluding a number of outputs at least equal to the number N of inputs,for routing an input signal to at least one output, each input beingadapted to receive signals modulating optical carriers having mdifferent wavelengths (λ₁, λ₂, . . . , λ_(m)); characterized in that itincludes: means (126 ₁₁, . . . , 126 _(NB); 226 ₁₁, . . . , 226 _(NB))for grouping all of the carriers received at an input of the switch intonon-contiguous subsets (S₁₁, . . . , S_(1B)) of carriers; selector units(129 ₁, . . . 129 _(NB); 229 ₁, . . . , 229 _(NB)) for routing in blocks(G₁₁, . . . , G_(NB)) the signals corresponding to each subset ofoptical carriers; and means (142, 145, 150) for dividing each subset andthen transmitting all the carriers of that subset to the same output ofthe switch.
 2. A switch according to claim 1, characterized in that itfurther includes: means (226 ₁, . . . , 226 _(N)) for grouping all thesubsets (S₁₁, . . . , S_(1B)) of carriers into non-contiguous groups(SG₁, . . . , SG_(N)) of subsets; means (229 ₁, . . . , 229 _(NB)) forrouting in blocks (H₁, . . . , H_(N)) the information corresponding to aplurality of subsets of carriers; and means (44, 45, 46; 54, 55; 206;305; 310) for selecting a single subset of carriers per output of theswitch.
 3. A switch according to claim 1, characterized in that itincludes means (124 ₁, . . . , 124 _(B)) for converting the wavelengthsof the carriers of each subset into predetermined wavelengths (λ′₁, . .. , λ′_(m/B)) in a spectral window substantially narrower than thewindow of the m wavelengths at the input of the switch, in order for theselector units (129 ₁, 129 ₂, . . . , 129 _(NB)) to process wavelengthsover a spectral window smaller than the spectral window of the mwavelengths at the input of the switch.
 4. A switch according to claim3, characterized in that it includes converter means after the selectorunits (129 ₁, 129 ₂, . . . , 129 _(NB)) for converting the wavelengths(λ′₁, λ′₂, . . . , λ′_(m/B)) of the carriers of each subset (S₁₁, . . ., S_(NB)) selected.
 5. A switch according to claim 1, characterized inthat it includes N.B selector units (122 ₁, . . . , 122 _(NB)), where Nis the number of inputs of the switch and B is the number of subsets ofcarriers received at the same input, and in that each selector unit (122₁, . . . , 122 _(NB)) includes N.B optical amplifiers (132 ₁, . . . ,132 _(NB)) each associated with a corresponding input of the selectorunit, said optical amplifier being activated to transmit the signalapplied to its input.
 6. A switch according to claim 1, characterized inthat it further includes variable delay means (130 ₁₁, 130 ₁₂, . . . ,130 _(N) _(²) _(B) _(²) ) associated with each selector unit (129 ₁, 129₂, . . . , 129 _(NB)) and controlled so as to delay the signal (G₁₁, . .. , G_(1B), . . . , G_(N1), . . . , G_(NB)) selected by said unit as afunction of the priority accorded to said signal.
 7. A switch accordingto claim 1, characterized in that it further includes amplifier means(128) on the input side of the selector units (129 ₁, 129 ₂, . . . , 129_(NB)) for amplifying the subsets of carriers.
 8. A switch according toclaim 2, characterized in that a selector unit (222 _(1a)) includes: Noptical gates (41 ₁, . . . , 41 _(N)) coupling N respective inputs ofthe selector unit to a coupler (42) having N inputs and one output; ademultiplexer (44) having an input coupled to the output of the coupler(42) and having N outputs; N optical gates (45 ₁, . . . , 45 _(m))coupled to respective outputs of the demultiplexer (44); and m/Bmultiplexers (46 ₁, . . . , 46 _(m/B)) each having B inputs and oneoutput, each input being connected to a respective output of thedemultiplexer (44), and the m/B outputs of said demultiplexersconstituting the outputs of the selector unit.
 9. A switch according toclaim 2, characterized in that a selector unit (222 _(1b)) includes: Noptical gates (50 ₁, . . . , 50 _(N)) divided into groups of N/p gates;each group of N/p gates is coupled to N/p respective inputs of theselector unit (221 b); p couplers (51 ₁, . . . , 51 _(p)) each havingN/p inputs coupled to N/p gates and having one output; p optical gates(52 ₁, . . . , 52 _(p)) having their inputs coupled to respectiveoutputs of the couplers (51₁, . . . , 51 _(p)); a coupler (53) having pinputs connected to respective outputs of the gates (52 ₁, . . . , 52_(p)) and having B outputs; B optical gates (54 ₁, . . . , 54 _(B))having their inputs coupled to respective outputs of the couplers (53);and a demultiplexer device (55) having B inputs connected to respectiveoutputs of B optical gates (54 ₁, . . . , 54 _(B)) and having m/Boutputs coupled to the outputs of the selector unit (222 _(1b)).
 10. Aswitch according to claim 2, characterized in that a selector unit (222_(1c)) includes: a space selector stage including N optical gates (201₁, . . . , 201 _(N)) divided into groups of N/p gates, said gates beingcoupled to N respective inputs of the selector unit (222 _(1c)); pcouplers (202 ₁, . . . , 202 _(p)) each having N/p inputs and oneoutput, said inputs being coupled to N/p respective outputs of a groupof optical gates (201 ₁, . . . , 201 _(N)) of the space selector stage;a cyclic first array of waveguides (203) having q inputs, where q isgreater than p, p inputs of the q inputs of said array being coupled top respective outputs of the couplers (202 ₁, . . . , 202 _(p)); a stagefor selecting subsets of carriers including B optical gates (204 ₁, . .. , 204 _(B)) having their inputs connected to B respective outputs ofthe first array of waveguides (203); m/B couplers (205 ₁, . . . , 205_(p)) each having B²/m inputs and one output, said B²/m inputs beingcoupled to respective outputs of the first array of waveguides (203) viaoptical gates (204_(i)); and a cyclic second array of waveguides (206)having m/B inputs coupled to m/B respective outputs of the couplers (205₁, . . . , 205 _(m/B)) and having m/B outputs coupled to the outputs ofthe selector unit (222 _(1c)).
 11. A switch according to claim 2,characterized in that a selector unit (222 _(1d)) includes: a spaceselector stage including N optical gates (301 ₁, . . . , 301 _(N))divided into groups of N.B/q gates each corresponding to a comb ofwavelengths; q/B couplers (302 ₁, . . . , 302 _(q/B)) each having N.B/qinputs and B outputs, the inputs of each coupler being coupled to theoutputs of the optical gates (301 ₁, . . . , 301 _(N)) of the spaceselector stage; a stage for selecting a subset of carriers consisting ofq optical gates (304 ₁, . . . , 304 _(q)) having inputs connected torespective outputs of the couplers (302 ₁, . . . , 302 _(q/B)); and ademultiplexer (305) having q inputs connected to q respective outputs ofthe gates (303 ₁, . . . , 303 _(q)) of the stage for selecting a subsetof carriers and having at least m/B outputs coupled to the outputs ofthe selector unit (222 _(1d)), q being chosen to be greater than m. 12.A switch according to claim 11, characterized in that a selector unituses the same array (310) for two switching stages (SS_(2h), SS_(2h+1)),said array being used bidirectionally.
 13. A switch according to claim11, characterized in that a selector unit (222 _(1d)) further includes qoptical filters (303 ₁, . . . , 303 _(q)) coupling q respective outputsof the couplers (302 ₁, . . . , 302 _(q/B)) to the inputs of the qoptical gates (304 ₁, . . . , 304 _(q)) of the stage for selecting asubset of carriers.